Nobody said this (well, besides you :-).
There is a quote which (in various phrasing) is often attributed to Winston Churchill, but (of course) this quote mentions neither "Democrats" nor "Republicans" since being a Brit he would not have thought in those terms. The quote people cite mentions "liberals" and "conservatives", and further, if Churchill actually said it, he would have meant something quite different by the word "liberal" (and for that matter "conservative") than most Americans do today.
Furthermore, there is some doubt as to whether Churchill ever said such a thing.
And besides, I've always disagreed with that quote, whoever said or didn't say it, and however it is phrased.